Palmlike Plants from the Dolores Formation (Triassic) Southwestern Colorado
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Palmlike Plants from the Dolores Formation (Triassic) Southwestern Colorado GEOLOGICAL SURVEY PROFESSIONAL PAPER 274-H Palmlike Plants from the Dolores Formation (Triassic) Southwestern Colorado By ROLAND W. BROWN A SHORTER CONTRIBUTION TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 274-H UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1956 UNITED STATES DEPARTMENT OF THE INTERIOR Douglas McKay, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. CONTENTS Page Page Abstract.-_________________________________________ 205 Relationships of Sanmiguelia^-- ______________________ 207 Geologic occurrence of the plants.____________________ 205 Bibliography.___________________-_-___-___-_-----_- 209 Description of the specimens,________________________ 206 ILLUSTRATIONS Page FIGURE 29. Reconstruction of Sanmiguelia lewisi Brown_____________ ______________________________________________ 206 PLATES 32, 33. Triassic plants from southwestern Colorado ___________________________________-------_-- _ -Following 206 in A SHORTER CONTRIBUTION TO GENERAL GEOLOGY PALMLIKE PLANTS FROM THE DOLORES FORMATION (TRIASSIC) IN SOUTHWESTERN COLORADO By KOLAND W. BROWN ABSTRACT Partial section at old Fall Creek post office, Colorado Plant remains from the Dolores formation in southwestern Colorado include a few small twigs of the conifer Brachyphyllum Jurassic and large, many-ribbed leaves described as those of an angio- Entrada sandstone. 50 ft. Whitish massive sandstones with sperm, tentatively regarded as a primitive palm and named few dark, shaly or limy thin-bedded strata. Sanmiguelia lewisi. This is the earliest known angiospermous Triassic flowering plant. Its occurrence in the Middle to Late Triassic, Dolores formation. 485 ft. Bright red, calcareous, massive however, indicates that evidence for the origin of the angio- and thin-bedded cliff-forming sandstones, few shales, sperms should be looked for in the earlier Triassic or late and some conglomerates. It yields remains of meto- Paleozoic. posaurs, phytosaurs, and plants. The lowermost whitish conglomeratic sandstone rests on an erosion GEOLOGIC OCCURRENCE OF THE PLANTS surface of the Cutler formation. Permian In September 1953, G. Edward Lewis, of the U. S. Cutler formation. 275 ft. Dark red shales and sandstones, Geological Survey, searching for fossil remains in the with fragmentary plants. upper part of the San Miguel Kiver valley in south The Dolores formation, named and described by western Colorado, found a palmlike leaf impression in Whitman Cross (1899) from exposures in the valley of the red Dolores formation near Placerville. This Dolores River in southwestern Colorado, at first specimen, 38 cm long and 20 cm wide, was fragmentary, included the red beds that are now known as the Cutler lacking the apex and base. Therefore, further search formation. However, the discovery in 1904 near was made at the same locality early in 1954, but Lewis Ouray of an angular unconformity below the fossili- found only a few more fragments, none of which gave ferous horizon in the Dolores caused Cross and his a clue to the nature of the basal or petiolar portion of associates (Cross, Howe, Ransome, 1905; Cross, the leaves. However, in September 1954, Lewis and Ransome, 1905; Cross, Howe, Irving, 1907) to restrict the writer, at an outcrop one-half mile north of the the name Dolores to the Triassic strata and to name original site, succeeded in finding fairly good specimens the more reddish underlying beds the Cutler formation, that illustrate the salient features of these leaves, provisionally of Permian age. Cross reported that some of which were still attached to part of a structure R. C. Hills in 1880 and 1882 had announced the dis less cast of a stem. Further exploration of the fossil- covery of fossils in the Dolores, including reptilian bearing bed along its outcrop for 10 miles on both sides teeth, ganoid fishes, mollusks, ana plants. Before of the San Miguel Kiver yielded equally good material these could be described, however, they were lost. to the writer in June, 1955. Cross said that in the course of his survey of the area The principal locality is in SE% sec. 12, T. 43 N., R. more reptilian teeth and a plant, identified by David 11 W., in a low cliff of reddish calcareous sandstone, on White as Pachyphyllum [an error for Brachyphyllum] the hillside of the right bank, 420 feet above the San munsteri, were found. All of these fossils reputedly Miguel Kiver and 145 feet above the base of the indicated the Triassic age of the Dolores. At the Fall Dolores formation, near the old Fall Creek post office, Creek post office locality in the Dolores the writer and about 2% miles southeast of Placerville. Exposed there Lewis in 1954 found phytosaurian teeth and the plant is the following pertinent sequence of strata, omitting impressions described in the following pages, including the overlying 1000 feet of the Jurassic Wanakah and the object of unknown identity (pi. 33, fig. 4). Morrison formations, and 250 feet of the Cretaceous The nonmarine sediments of the Triassic in the "four Dakota sandstone: corners" area of the southwestern States are believed 364884—56 205 206 SHORTER CONTRIBUTIONS TO GENERAL ASSEMBLY FIGURE 29. Tentative reconstruction of Sanmiguelia lewisi Brown. In life the leaves were probably somewhat stiff, like the lower right hand leaf, rather than undulant. No sheaths or crests are shown because discernible evidence for them is lacking. X 1/5 to have accumulated on floodplains and in scattered Numerous species of conifers have been described pools and lakes at not many hundreds of feet above sea from the Triassic of the United States, and particularly level. Such plants, therefore, as were entombed in the from the southwestern States, notably in and around sediments, most likely originated in the lowlands of the Petrified Forest National Monument near Hoi- the basin of deposition, whereas remains of more dis brook, Arizona. There is, therefore, nothing especially tant upland plants did not get into the fossil record. unusual about the presence of such remains in the Whatever the reason, whether land vegetation was Triassic of southwestern Colorado. sparse on account of climatic conditions, or whether the circumstances attending the accumulation of the MONOCOTYLEDONS sediments were unfavorable, plant remains in the SANMIGUELIA Brown, n. gen. Dolores apparently are relatively scarce. Plants with alternate, simple, large, elliptic, strongly DESCRIPTION OF THE SPECIMENS pleated, monocotyledonous, palmlike leaves. Stem CONIFERS rounded, tapering rapidly toward the apex, but other Brachyphyllum miinsteri Schenk features unknown. Plate 33, figures 1, 3 Sanmiguelia lewisi Brown, n. sp. Brachyphyllum miinsteri Schenk, 1867, Die fossile flora der Grenz- Plate 32, figures 1, 2; plate 33, figure 2 schichten des Keupers und Lias Frankens, p. 187, pi. 43, figs. 1-12. Elliptic to ovate entire, firm-textured leaves, attain The coniferous twigs from the Dolores formation, ing a length of 40 cm and width of 25 cm, conspicu here figured, resemble closely those shown by Schenk ously pleated, the strong ribs or veins converging from the Rhaetic formation at Bamberg, Germany. toward the apex and the base. Midrib not differen Neither these nor Schenk's specimens, however, quite tiated. Between the 16 to 20 ribs are closely spaced match the usual conception of the features of the genus parallel veinlets, as in all palms. The leaves are at Brachyphyllum with its closely appressed foliage. They tached to the stem alternately by broad, thin, clasping, can be compared with the twigs of some species of or probably sheathing petioles at vertical intervals of Palissya, Sequoia, Sphenolepidium, Araucarites, and 4 cm, as shown by three leaves preserved in one block others found in the Triassic and later formations. of sandstone. These permit a tentative reconstruction Without cones or other distinguishing features, the of the plant (fig. 29). However, neither sheaths nor identification of remains of this kind is fraught with crests (hastulas, ligules) are discernible, either because much uncertainty. Probably the specimen collected none existed or because the preservation around the by Cross (1899) in the Telluride quadrangle and identi stem is poor. The stem, now only a calcitic cast fied by David White as Pachyphyllum munsteri, was without cell structure, is rounded and in a vertical dis a representative of this species—the Pachyphyllum tance of 10 cm narrows rapidly from a diameter of 4 being an error for Brachyphyllum. Apparently, that cm to a blunt point, thus suggesting that it is the apical specimen is now lost. portion of a low, but mature plant. PLATE 32 FIGURES 1, 2. Sanmiguelia lewisi Brown. Fig. 1 shows the broad base of the petiole clasping the grayish, granular, rounded stem. The latter is a calcitic cast without cellular structure. X % GEOLOGICAL SURVEY PROFESSIONAL PAPER 274 PLATE 32 TRIASSIC PLANTS FROM SOUTHWESTERN COLORADO GEOLOGICAL SURVEY PEOFESSIONAL PAPER 274 PLATE 33 TRIASSIC PLANTS FROM SOUTHWESTERN COLORADO PALMLIKE PLANTS FROM DOLORES FORMATION 207 The generic term Sanmiguelia is feminine and is from This is a further demonstration of the primitive nature of the the name of the river at the type locality. The species entire type * * *. In Latania commersoni J. F. Gmel. (L. borbonica Lam.), the seed-leaf is ovate, lanceolate (pi. 23, fig. is named for G. Edward Lewis, vertebrate paleontologist 94); during growth the later leaves become relatively broader, of the U. S. Geological Survey and discoverer of the until, by distal tension, splits take place (pi. 23, fig. 93), and in first specimens. the adult the leaf is a quite broad, fan-leaf type * * *. In the growth of a pinnate-leaved palm, when a new leaf first appears, RELATIONSHIPS OF SANMIGUELIA the pinnae cling together laterally on their outer margin and to / the distal leaflet, in such a way that the whole leaf simulates the Sanmiguelia leurisi is regarded tentatively but credi entire type and demonstrates the simple dynamic genesis of this bly as a primitive palm.